96 



water- vapour ; (3) alcoholic solution of caustic 

 potash, which also absorbs bisulphide of carbon ; 

 (4) alkalinised solution of pyrogallol oxygen ; (5) 

 phosphorus oxygen ; ( 6 ) cuprous chloride dissolved 

 in hydrochloric acid oxygen, carbonic oxide, 

 acetylene, and allylene ; ( 7 ) the same dissolved in 

 ammonia, which absorbs also the hydrocarbons of 

 the olefine series ; ( 8 ) dilute sulphuric acid 

 ammonia, methyl-amine, and other amines; (9) 

 strong sulphuric acid water, alcohol, methyl Aether, 

 propylene and its homologues ; ethylene slowly, 

 hydrogen and marsh gas not at all; (10) Nord- 

 hausen sulphuric acid, which absorbs the olefines, 

 not hydrogen or the marsh-gas series; (11) con- 

 centrated aqueous solution of sulphate of iron, 

 which absorbs nitric oxide ; ( 12) bromine, which in 

 presence of water acts like Nordhiiusen sulphuric 

 acid; (13) sulphur, which absorbs sulphuretted 

 hydrogen, sulphurous acid, and bisulphide of 

 carbon; (14) chromous sulphate, to which am- 

 monium chloride and ammonia have been added, 

 absorbs oxygen, nitric oxide, acetylene, and 

 allylene ; ( 15 ) alcohol absorbs chloride of cyanogen, 

 methyl chloride, methyl ether, and cyanogen ; ( 16) 

 mercuric oxide cyanogen; (17) lead acetate 

 sulphuretted hydrogen; (18) lead peroxide sul- 

 phurous acid. Analyses conducted by the aid of 

 such reagents are direct ; and on the same principle 

 of observation of shrinkage we may also employ 

 explosion-reactions. In the case of air we take a 

 measured volume and add to it about half its bulk 

 of hydrogen, observing precisely Avhat volume we 

 add. In this case the graduated tubular vessel, in 

 which the gas is contained, has two platinum wires 

 fused into it so as to approach one another within 

 the vessel ; our vessel is then called a Eudiometer. 

 An electric spark is made to leap across the 

 interval between the two wires ; an explosion 

 occurs ; part of the hydrogen of the mixture com- 

 bines with the whole of the oxygen ; presently the 

 aqueous vapour formed condenses, and the volume 

 of the mixture becomes, at the former tempera- 

 ture and pressure, considerably less than it was 

 before the explosion. The shrinkage is measured ; 

 the gas which has disappeared consisted, for every 

 three volumes, of two of hydrogen and one of 

 oxygen. One-third of the shrinkage, therefore, 

 represents the amount of oxygen present in the air 

 acted upon ; and in the case of air the balance of 

 the original volume is taken (if the air had been 

 freed from moisture and carbonic acid ) as consist- 

 ing wholly of nitrogen (including argon). In more 

 complicated mixtures the explosion-reactions lead 

 to more complicated processes and calculations. 

 For example, if we have a mixture of hydrogen, 

 methane, carbonic oxide, and nitrogen (which cor- 

 responds to coal-gas that has been passed through 

 potash solution and has stood over strong oil of 

 vitriol), we first explode a known volume of the 

 mixture with an excess of oxygen. The shrinkage 

 is observed, and then potash solution is introduced 

 in order to remove the carbonic acid formed by the 

 combustion of the methane and the carbonic oxide. 

 The nitrogen alone now remains, together with 

 the excess of oxygen ; and the amount of the 

 latter is determined by another explosion with 

 hydrogen, whence the amount of nitrogen may be 

 determined ; and from this we find the volume of 

 combustible gas originally present in the mixture. 

 We now know ( 1 ) the volume originally used ( A) ; 

 (2) the volume of combustible gas therein con- 

 tained (B); (3) the contraction of volume on 

 explosion (C) ; and (4) the volume of carbonic acid 

 generated on explosion (D). We also know that 

 when hydrogen is exploded with an excess of 

 oxygen the combustion of one volume of hydrogen 

 causes the condensation of 1 volume of the 

 mixture ; that the combustion of 1 volume of 



carbonic oxide similarly causes a shrinkage of 

 volume, and the production of 1 volume of 

 carbonic acid ; and that the combustion of 1 

 volume of methane (light carburetted hydrogen, 

 marsh-gas, CH 4 ) produces a shrinkage of 2 volumes 

 and the formation of 1 volume of CO.,. Hence we 

 find that the shrinkage C is made np of the original 

 H-volume x H, phis the CO-volume x J, phis 

 the CH 4 - volume x 2 ; and that the carbonic acid 

 (= D) is equal to the CO-volume plus the CH 4 

 volume ; and if we set down these statements 

 algebraically, writing ID for the original volume of 

 nitrogen, x for that of hydrogen, y and z for those 

 of carbonic oxide and marsh-gas, we have the 

 equations A = w + x + y + z; B = x + y + z; D 



= y + z; and C = ~ + | + z, from which w, x, 



y, z may be readily found and thereafter reduced 

 ito percentages. If any of these quantities, iv, x, 

 y, z, be found equal to (or to a small negative 

 quantity ), the corresponding gas is not present in 

 the mixture. 



The apparatus made use of varies from a simple 

 graduated tubular vessel to the more elaborate 

 compensating apparatus now in use. The object 

 of compensation is to enable the volume of the gas 

 to be ascertained without 

 calculation for correction. 

 We may refer by way of 

 illustration to the ap- 

 paratus of Frankland and 

 Ward, which is fully ex- 

 plained in Williams' Hand- 

 book of Chemical Manipu- 

 lation, as well as in Messrs 

 Frankland and Ward's 

 memoir in the Quarterly 

 Journal of the Chemical 

 Society. We take as an 

 example an explosion- 

 analysis of atmospheric 

 air. A few ( three or four ) 

 cubic inches of air, freed 

 from carbonic acid, having 

 been introduced into the 

 tube, I, it is transferred 

 into F for measurement 

 by opening the cocks, 

 I, /', and placing the tube, 

 F, in connection with the 

 exit-pipe, h ; the trans- 

 ference can be assisted, 

 if necessary, by elevating 

 the mercurial trough, C. 

 (The part marked b in 

 the figure is merely the 

 tubular well of the mer- 

 curial trough, C.) When 

 the air, followed by a few 

 drops of mercury, has 

 passed completely into F, 

 the cock, I, is shut, and/ 

 turned, so as to connect F 

 and H with h. Mercury 

 is allowed to flow out 

 until a vacuum of two or 

 three inches in length is 

 formed in H, and the 

 metal in F is just below 

 one of the graduated 

 divisions ; the cock, /, is 

 then reversed, and mer- 

 cury very gradually ad- 

 mitted from G, until the highest point in F exactly 

 corresponds with one of the divisions upon that 

 tube ; we will assume it to be the sixth division, 

 there being ten divisions in all. This adjustment 

 of mercury, and the subsequent readings, can be very 



O O 



A, a tripod, with levelling 

 screws ; BB, a vertical pil- 

 lar, to which is attached 

 C, a mercurial trough, mov- 

 able by a rack and pinion, 

 a; DD, a glass cylinder, 

 36 inches long, with an in- 

 ternal diameter of 4 inches, 

 containing three tubes, F, 

 G, H, which communicate 

 with one another, and with 

 the exit-pipe, h, by the ap- 

 paratus E/E. The rest of 

 the figure will be sufficiently 

 intelligible fromthedescrip- 

 tion given in the text. 



